This invention relates to an easily opened closure suitable for use with a container which includes a layer of plastic. The closure may be of a multi-layer construction or may include a layer of barrier material. If an all-plastic closure is used with an all-plastic container, the container and closure assembly is especially suitable for microwaving.
This application is a continuation-in-part of U.S. Ser. No. 07/534,200, which is herein incorporated by reference. Both applications are owned by the same assignee.
Microwavable containers are growing in popularity because they not only replace the storage function of the traditional can, but also enable the consumer to heat the contents in the container and to eat from the container.
In the prior art, closures for microwavable containers generally included both a double seamed metal lid and a plastic overcap. The metal lid is double seamed onto the all-plastic container and has a score line in the metal lid. To open the metal lid, the consumer has to pull hard enough to break the metal score line and in doing so often splatters the food from the container. Additionally, a residual rim of metal remains affixed to the top edge of the container after opening and removing the lid. The overcap is then snapped over the remaining rim and the container and overcap are placed in the microwave.
The residual metal rim of the prior art container is undesirable because it has a sharp edge, making it prone to cut the fingers of those using the containers, especially children for whom the microwavable containers are particularly convenient.
The residual metal also makes recycling the container more difficult. While it is theoretically possible to recycle such containers, there is presently no system which provides for recycling of mixed plastic and metal containers. Neither is there a widespread recycling service that collects such containers. By providing an all-plastic closure for use with an all-plastic container, both closure and container will be recyclable as plastic. There are a number of technologies which use such recycled plastic in an interior layer of a container. Additionally, the code requirements for such plastics and recycling centers for such plastics are generally established.
The prior art closure system also requires a large number of consumer steps for using the container: removing the overcap, opening the metal lid, replacing the overcap, placing the container in the microwave oven, heating the container and contents in the microwave oven, and removing the cap to gain access to the food.
The overcap of the prior art has a number of characteristics necessary so that it can be used with a microwavable container. The center panel of the overcap is raised well above the top of the metal lid. A number of holes are punched in the center of the lid, and the overcap is sized so that it fits tightly with the outside of the container.
These modifications are required because of the unique way in which the microwave oven heats food in containers. The food is generally filled to the top of a microwavable container, making the raised overcap necessary to accommodate expansion of the food caused by steam bubbles. The holes in the lid allow for steam venting. Microwave heating causes explosive boiling in the food which creates splattering and can be so violent as to physically move the container. This is a type of localized superheating which does not occur in conventional cooking where heating is by conduction. The conventional stovetop cooking causes a more uniform, gentle heating which is unlikely to produce explosions.
The overcap of the prior art must be tight-fitting to reduce the likelihood of explosions causing it to blow off of the container. However, this also makes removal of the lid more difficult, especially for elderly persons and young children.
Other types of prior art closures included thermoplastic material molded onto composite materials, such as shown in U.S. Pat. No. 4,456,146. However, such container assemblies do not address the problems involved with microwave heating an open container, as will be discussed later.
This invention solves these problems of the prior art microwavable containers and closures. While the closure and container are particularly beneficial for a package intended to be microwaved, the easy-open features are useful for a wide variety of food containers, including shelf stable foods; retortable packages; hot filled products, such as juice; or frozen foods, such as for juice concentrate. The container may be of a bowl shape, such as shown in the detailed embodiments herein, or of any other suitable shape, for example, a tapered cylinder.